FIG. 7A is a schematic view of air paths of a heat exchange operation in the prior art;
FIG. 7B is a schematic view of air paths of an air exhaust operation in the prior art.
Now, the prior art is described with reference to FIGS. 7A and 7B. A conventional total heat exchange device 101 performs a heat exchange operation and an air exhaust operation. In the heat exchange operation, air is directed from an indoor exhaust port 106 to an outdoor discharge port 105 through an exhaust air path 109 and the air is directed from an outdoor suction port 104 to an indoor intake port 107 through an intake air path 108, and at the same time, heat exchange is performed between the air passing along the exhaust air path and the air passing along the intake air path. In the air exhaust operation, air sucked from the indoor exhaust port 106 is discharged from the outdoor discharge port 105 through a heat exchange element 114.
The above-described conventional total heat exchange device performs merely the heat exchange operation and the air exhaust operation. In case that an outdoor temperature in winter is very low (below zero), the total heat exchange device will be operated with an air exhaust operation of a low flow rate, to prevent the heat exchange element from being frozen. If the total heat exchange device is operated with an air exhaust operation of a low flow rate for a long time, it is possible that the amount of indoor ventilation is inadequate, such that indoor air quality is deteriorated, which makes the user feel uncomfortable.